This invention relates to a tape cassette comprising a magnetic tape coiled around a pair of tape reels rotatably mounted within a pair of cassette halves making up a cassette main body. More particularly, it relates to such tape cassette so designed and arranged that a discrimination may be made as to whether the tape cassette loaded on a recording/reproducing apparatus is used exclusively for recording video signals or used for recording data signals.
In general, a detection method employing optical means is adopted for detecting a leading end or a trailing end of an elongated magnetic tape contained within the cassette halves making up the tape cassette.
For implementing the detection method employing such optical means, the cassette halves containing the magnetic tape therein is formed with openings facing light emitting devices arranged on the recording/reproducing apparatus. These openings are formed so as to be positioned intermediate between a pair of tape reels rotatably mounted within the cassette halves. On the other hand, the opposite lateral sides of the cassette halves are formed with light-transmitting apertures through which the light from the light emitting devices facing the inside of the cassette halves via the above openings may be transmitted to outside of the cassette halves via the interposed magnetic tape. The recording/reproducing apparatus is provided with light-receiving devices (photodetector devices) for detecting the light transmitted through the light-transmitting apertures formed in the cassette halves. The state of light transmitted through the light-transmitting apertures is detected by these light receiving devices for detecting the leading and trailing ends of the magnetic tape. That is, the leading and trailing ends of the magnetic tape, contained within the cassette halves, are connected to tape leaders having a sufficiently proven mechanical strength. It is by these tape leaders that the magnetic tape is attached to the tape reels. The magnetic tape coated with a magnetic recording medium has a light transmittance different from that of the tape leader not coated with a magnetic recording medium. Specifically, the light transmittance of the magnetic tape to the light of a wavelength of 800 to 900 nm is not higher than 60%, while that of the tape leader to the same light is not less than 60%. With the detection method employing optical means, the leading and trailing ends of the magnetic tape are discriminated from each other based on the difference in light transmittance between the magnetic tape and the tape leader.
In the method for detecting the leading and trailing ends of the magnetic tape employing the above-mentioned light-emitting and light-receiving devices, the light from the light-emitting device facing the inside of the cassette halves is received by each light receiving device. The amount of light received by the light-receiving device mounted on the tape supplying tape reel is compared to that received by the light-receiving device mounted on;the tape take-up tape reel. If a detection output by the light-receiving device mounted on the tape supplying tape reel is larger than that by the light-receiving device mounted on the tape take-up tape reel, the tape end is decided to be the leading end. If otherwise, the tape end is decided to be the trailing end. In other words, the tape end is found to be the leading end or the trailing end depending on which of the light-receiving devices has detected the high light transmittance tape leader connected to the leading or trailing end of the magnetic tape. Meanwhile, if detection outputs by the light-receiving devices are equal, a decision is given that the magnetic tape is in a running state.
It should be noted that the tape cassette containing a magnetic tape having a tape width of 8 mm is classed into the tape cassette exclusively employed for recording of picture signals and the tape cassette exclusively employed for recording of data signals, with the cassette halves being used in common with these two tape cassette types. These two types of the tape cassettes are extremely difficult to discern from each other as long as the appearance of the tape cassette is concerned. Besides, the magnetic tape contained in the tape cassette dedicated to the recording of picture signals is different in type from the magnetic tape contained in the tape cassette dedicated to the recording of picture signals. Consequently, should the tape cassette for picture signals be used for recording .the tiara signals, it may occur that the recording capacity falls short such that required data can not be recorded. Besides, the magnetic tape for picture signals has an error rate security different from that of the magnetic tape for data signals, so that dropout of recording data signals tends to be incurred if the tape cassette for picture signals be used for recording data signals.